The present invention broadly relates to a new and improved apparatus for the dosing of solid materials, and more specifically, pertains to a new and improved apparatus for the dosing of a pulverulent solid material.
Generally speaking, the dosing apparatus of the present invention comprises a container for receiving the solid material and in which there is positioned a distributor element equipped with a conveyor member and operatively connected with a drive shaft for rotation in both directions. A rotary diaphragm is arranged below the distributor element. A base plate is operatively associated with and located below the rotary diaphragm. The rotary diaphragm and the base plate are rotatable relative to each other through an angle less than a full revolution. The rotary diaphragm and the base plate are each provided with at least one opening for the through-passage of the solid material. These openings can be closed by rotating the rotary diaphragm and the base plate relative to one another.
Such type of dosing apparatus is described in an early construction in U.S. Pat. No. 909,657 of Thomas S. Patterson, granted Jan. 12, 1909. The basic principle was applied in a dispenser for pulverulent to diaphragms control the dosed delivery and a simultaneously moved agitator allows the solid material to freely flow in the region of receiving and through-passage openings.
A substantial improvement of this principle, particularly in connection with an automated operation, was disclosed a good seventy years later by Pavel Lehky and Marie Lehky in Swiss Patent No. 633,884, published Dec. 31, 1982. The pulverulent material introduced into the container is distributed on a perforated diaphragm by means of a motor-driven conical distributor element and through which the pulverulent material can depart from the dosing apparatus. The pulverulent material is transported by a spiral shaped conveyor member which moves the material from the periphery to an opening in the middle of the perforated diaphragm.
The undesirable possibility exists with the aforementioned prior art dosing apparatus utilizing the aforedescribed motor drive and thus providing a substantially improved apparatus which can be employed in an automated operation, that during filling of such dosing apparatus with pulverulent solid material possessing very fluent or free-flowing properties, a part of such material will automatically move to the outlet opening or port and, without any rotary motion of the conveyor member, fall through the outlet opening or port and into, for example, a laboratory reactor.
This uncontrolled delivery or dosage could be avoided if it were possible to provide, in the sense of the Patterson dispenser, a closure diaphragm instead of only the perforated diaphragm used in Lehky's dosing apparatus. This closure diaphragm could be then opened and closed by the motor, since it concerns a motor-driven apparatus for automated operation.
However, it has been found that a satisfactory solution is not reached by simply combining a motor-driven distributor system with a rotary diaphragm which, in fact, can be found also in manually operated containers for spices or the like. The reason for this is that if pulverulent material is to pass through a closed rotary diaphragm, it is necessary to first open the rotary diaphragm by rotating it through a predetermined aperture angle. When the rotary diaphragm is open, the rotation must be continued because now the spiral-shaped conveyor member becomes effective by conveying material flowing in at the periphery towards the central zone of the open diaphragm. This means that after the opening operation a type of slip coupling between the motor and the rotary diaphragm should make this further motion possible.
It is well known that an environment containing dust and powder is not at all ideal for using a slip coupling. In the case of a laboratory dispenser there is the further unfavorable factor that all sorts of abrasive and chemically aggressive materials, but also materials which intensify sliding or adhesion properties, should be dosed by this apparatus, so that a controlled coupling action can only be expected when the coupling can be kept free from the influence of such materials. Naturally, this leads to sealing problems and increased costs for the manufacture and maintenance of the apparatus. Reliability in operation remains questionable.